The present invention relates generally to devices for implantation within a patient""s body, and more particularly to devices for activating, deactivating, and/or controlling implants located within a body that monitor physiological conditions and/or provide therapeutic functions.
Devices are known that may be implanted within a patient""s body to monitor one or more physiological conditions and/or to provide therapeutic functions. For example, sensors or transducers may be located deep within the body for monitoring a variety of properties, such as temperature, pressure, strain, fluid flow, chemical properties, electrical properties, magnetic properties, and the like. In addition, devices may be implanted that perform one or more therapeutic functions, such as drug delivery, defibrillation, electrical stimulation, and the like.
Often it is desirable to control by external command such devices once they are implanted within a patient, for example, to obtain data, and/or to activate or otherwise control the implant. An implant may include wire leads from the implant to an exterior surface of the patient, thereby allowing an external controller or other device to be directly coupled to the implant. Alternatively, the implant may be remotely controlled, for example, using an external induction device. For example, an external radio frequency (RF) transmitter may be used to communicate with the implant. RF energy, however, may only penetrate a few millimeters into a body, because of the body""s dielectric nature, and therefore may not be able to communicate effectively with an implant that is located deep within the body. In addition, although an RF transmitter may be able to induce a current within an implant, the implant""s receiving antenna, generally a low impedance coil, may generate a voltage that is too low to provide a reliable switching mechanism.
In a further alternative, electromagnetic energy may be used to switch or otherwise control an implant, since a body generally does not attenuate magnetic fields. The presence of external magnetic fields encountered by the patient during normal activity, however, may expose the patient to the risk of false positives, i.e., accidental activation or deactivation of the implant. Furthermore, external electromagnetic systems may be cumbersome and may not be able to effectively transfer coded information to an implant.
Accordingly, it is believed that a device that overcomes these problems and/or that may more effectively remotely activate or otherwise control an implant located within a patient""s body may be considered useful.
The present invention is generally directed to implants that may be surgically or otherwise located within a mammalian body for monitoring one or more physiological parameters and/or for performing one or more therapeutic functions. For example, an implant in accordance with the present invention may be used for atrial defibrillation, pain relief stimulation, neuro-stimulation, drug release, activation of a light source for photodynamic therapy, monitoring of a radiation dose including ionizing, magnetic or acoustic radiation, monitoring of flow in a bypass graft, producing cell oxygenation and membrane electroportation, and measurement of various physiological parameters including heart chamber pressure, infraction temperature, intracranial pressure, electrical impedance, position, orthopedic implant strain or pH.
In a accordance with a first aspect of the present invention, an implant is provided that includes an electrical circuit configured for performing one or more commands when the implant is activated, an energy storage device, and a switch coupled to the electrical circuit and the energy storage device. An acoustic transducer is coupled to the switch that may be activated upon acoustic excitation by an external acoustic energy source for closing the switch to allow current flow from the energy storage device to the electrical circuit.
In one embodiment, the switch may be closed only when the acoustic transducer receives a first acoustic initiation signal followed by a second acoustic confirmation signal, the first and second acoustic signals being separated by a predetermined delay.
The switch may remain closed for a predetermined time and then automatically open. Alternatively or in addition, the switch may be opened when an acoustic termination signal is received by the acoustic transducer for discontinuing current flow from the energy storage device to the electrical circuit.
In one preferred embodiment, the electrical circuit includes a sensor for measuring a physiological parameter within the body. A transmitter or the acoustic transducer itself may be coupled to the electrical circuit for receiving an electrical signal proportional to the physiological parameter measured by the sensor. The transmitter or acoustic transducer may transmit a signal including information regarding the physiological parameter to a receiver located outside the body. Preferably, the sensor is a biosensor configured for measuring at least one of blood pressure, heart chamber pressure, infraction temperature, intracranial pressure, electrical impedance, position, orthopedic implant strain, or pH, and the acoustic transducer enables communication of data from the sensor to a receiver located outside the body.
In another preferred embodiment, the electrical circuit includes an actuator for activating or controlling a therapeutic device within the body that is connected to or otherwise associated with the actuator. The electrical circuit may activate the therapeutic device for a predetermined time, or until the switch is opened. Alternatively, the electrical circuit may control the therapeutic device in response to a physiological parameter measured by a biosensor coupled to the electrical circuit.
During use, the acoustic transducer may receive a relatively low frequency acoustic signal that vibrates the piezoelectric layer at its resonant frequency. The acoustic signal closes the switch, activating the implant from its xe2x80x9csleepxe2x80x9d mode to an xe2x80x9cactivexe2x80x9d mode. In the sleep mode, the implant may wait substantially indefinitely with substantially no energy consumption. Once activated, i.e., when the switch is closed, the electrical circuit performs one or more commands, such as measuring a physiological parameter within the body, or controlling a therapeutic device within the body. A signal proportional to the physiological parameter may be transmitted from the implant to a receiver located outside the body. Alternatively, the therapeutic device may be controlled based upon the physiological parameter.
In a further alternative, a set of command signals may be sent from a source outside the body along with or after the acoustic activation signal. The command signals may be interpreted by the electrical circuit to provide a set of commands to control the therapeutic device, e.g., to provide a desired course of treatment. For example, the commands may instruct the therapeutic device to provide a desired dosage for a desired duration, and/or may modify dosage or duration based upon feedback from the biosensor.